Spatial frequency filtering in an optical imaging system with an extended incoherent light source

A single-lens imaging system is described that provides spatial frequency filtering to an extended incoherent light source. Two ways to calculate the modified image are considered: First, the image is derived from the filtered diffraction pattern by Fourier synthesis. Second, the convolution of the object function with a Fourier transform of the filter function has to be evaluated with regard to a phase function that corresponds to the light source position.